Hepatic gluconeogenesis is necessary during starvation, stress and is accelerated in diabetes mellitus; it is regulated by changes in substrate and cofactor concentrations and enzyme activities, in turn regulated by hormones. Regulation of this process has been studied mainly in rats. Studies with other species suggest that rats may be a somewhat improper model for gluconeogenesis in humans due to such things as a diference in cellular location of phosphoenolpyruvate carboxykinase (PEPCK) and in the redox state of their mitochondria. Fatty acids enhance gluconeogenesis in rats but exert no effect on or inhibit this process in other species. We find fasted rabbits to have a distribution of hepatic PEPCK similar to humans. Lactate- and dihydroxyacetone-derived gluconeogenesis in rabbits is enhanced by glucagon, epinephrine and cyclic AMP and regulation of gluconeogenesis appears somewhat different in rabbits vs rats. The major influence of these effectors in rabbbits appears to be on the interconversion of fructose 1,6-bisphosphate and fructose 6-phosphate. We will use perfused livers and hepatocytes to investigate questions such as; is the effect of epinephrine mediated via alpha- or beta-adrenergic sites; what are the gluconeogenic influences of these effectors on fructose 1,6-bisphosphatase, phosphofructokinase and/or pyruvate kinase and what are their influences on glycogenolysis as mediated by phosphorylase? The influences of somatostatin and Ca2+ alone and with various effectors will be examined for their own influences and for their potentials as tools to study mechanisms of action of other effectors. L-tryptophan and quinolinate inhibit hepatic gluconeogenesis and increase the assayable activity of PEPCK in normal rats and their perfused livers respectively; yet these two compounds are ineffective in diabetic rats. Structural and kinetic properties of PEPCK from normal, diabetic and tryptophan-treated rats will be investigated to explain this curious observation and also to define characteristics of a key enzyme of gluconeogenesis which heretofore has received little attention. We suggest that tryptophan may normally regulate gluconeogenesis and that such regulation is altered in diabetes. We will investigate exogenous quinolinate's ability to enter diabetic liver cells; also tryptophan's influence on gluconeogenesis in normal and diabetic mice gerbils and guinea pigs.